Method of carrier-frequency suppression



Maw 4% 192,5.

; 1,560,505 R m. DUNCAN, JR METHOD 05 61min FREQUENCY SUPPRESSION Filed Ma 192s 2 Sheets-Sheet 1 /20 a lay gwuewtoq Quanta Nov. 3, 1925.

R. D. DUNCAN, JR

METHOD or CARRIER FREQUENCY sufimzsszou Fila d Ray 19, 1925 2 Sheen -Sheet 2 Patented Nov. 3, 1925 UNITED $TATESS 1,550,505 PATENT OFFICE;

ROBERT D. DUNCAN, JR., OF EAST ORANGE"NEW JERSEY, ASSIGNOJR. TO WIRED RADIO INC., 0 NEW YORK, N. Y., A G0RECRJA'IFIOII 0F DEL KWAB EL METHOD OF CARRIER-FREQUENCY SUPPRESSION.

Application filed May 19, 1925. Serial No. 31,393.

To all who! it may concern:

Be it known that I. Romcn'r D. Duncan, Jr. a citizen of the United States, residing at East Orange, in the county of-Essex and State of New J erscy, hare invented a certain new and useful Improvement in a lllethod of Carrier-ldrequency Suppression, of which the following; is a specification.

My invention relates broadly to radio transmission systems, and more particularly to a method of suppressing the carrier wave "frequency in radio transmission;

@ne of the objects of my invention, is to provide a method of suppressing the transmission of the unmodulatcd component of the carrier wave botlrdurinc' and intermediate the signaling or modulating periods.

A second object of my invcntionis to provide a method of incompletely suppressing the transmission of the unmodulated component of the carrier frequency both during and intermediate the periods of modulation.

A third object of my invention is to pro ride a signaling system particnlarl y adapted for modulating frequencies covering the voice range and the musical scale, in which. the unmodulated carrier frequency component may be suppressed at the transmitting station by circuit arrangements which 1 pro ride associated with the modulating system.

Another object of my invention is to provide a three phase high frequency generating or amplit'yinc system at a transmitting station which is arranged to act upon a load circuit. with modulation nieans etlective upon one of the phases of the high frequency i generating or amplifying system to-cause the flowct' high frequency current in the load circuit, such as an antenna or a line wire system, only during the period of modulation, the arrangement of circuits be in; such that when inodulation is not taking place no current will llow in the load circuit, i. e., both during and intermediate the modulating periods the unmodulated component ol the carrier trequcncyis substantially suppressed. i

Still another object of my invention is to provided a multi-phase source of high trequency oscillations arranged to be modulator by a source of energy whereby signaling}; energy may be impressed upon a radiating antenna system or a carrier wave line wire system only during the modulation pd 'riocls without transmission of carrier wave intermediate the modulation periods.

A still further object of my invention is to provide a system of telephone communication wherein a three phase frequency source is employed establishing equal high frequency Voltages having different phases which are balanced in such manner that in the absence of modulation, current will not flow in the load circuit, but being arranged in such manner that when modulation takes place the balanced condition of the three phase source becomes disturbed and completely modulated high frequency current from the main source appears in the load circuit, thereby cnahling'the transmission of energy during periods of modulation while the umnodulated carrier frequency component is prevented at all times from reaching the load.

My invention may be applied toyarious types of carrier Wave transmission systems, that is, systems which relate to the trans mission of signals by radiation from an antenna system through space for reception at any number of outlying stations or the transmission of signals over line wire systoms, such as telephone, electric light, power, and other lines for reception at receiving stations associated with the line at various points.

1 effect the elimination of the carrier frequency transmission by means located at the transmitting station. My systcn'i as herein described is generally applicable both in space radio and wired radio, and I intend no limitations upon the uses to which my invention may be applied. It is desirable in communication systems to eliminate'tho carrier frequency both :tfr'om the "viewpoint of increasing the etlicicncy of transmission and for decreasing interferencenormally otl'eredby the existence of the carrier 'lrc qucn'cy. l. am aware of the Carson push pull amplification method of suppressing the carrier frequency but I depart radically from the Carson method as will be more fully pointed out hereinafter; I have particularly described my invention in connection with radio telephone communication systems.

it is fundamental and well known in the art or radio telephony that du ring module tion a band of high frequencies instead of a single frequency 15 transmit-ted. The width of this band depends upon the number of single .ti'equency components contained the modulatin source. For example, in the voice the' sing e frequency components may extend from 100 to 3000 cycles while with music the range may be from 15 to 10,000 cycles per second. For purposes of discussion it is convenient and usual to consider only a single frequency modulating source from which conclusion may be drawn, which may be modified as required to conform to the condition of a frequency band instead of a single frequency.

Expressed mathematically, a carrier fre- That is, with single frequency modulation the modulated wave will consist of three components, Viz: The unmodulated carrier.

component and two modulated components consisting respectively of the carrier freuency plus and the carrier frequency minus t 1e modulating frequency. In actual radio telephony of course instead of a single frequency modulating source there will be a band of-frequencies' and under this condition equation (2) is altered in the following respects:-T he first term (E,sin (at) remains unchanged. The second and third terms change from single frequency terms to terms each consisting of a series of frequencies, respectively representing the carrier frequency plus and the carrier frequency minus each of the low frequency components of the modulating source. There will then be transmitted the main frequency or unmodulated component, represented b the first term in (2) and two bands of frequencies falling above and below the main frequency.

quency E sin at if modulated by a low single frequency Ksin pt may be written in the well known form (1) {3:E1 (1+K sin pt) sin (at in which OEKEI is the percentage of modulation, and m=2w high frequency and pz2r modulating frequency. By trigonometric trans formation equation (1) may be rewritten as follows:

cos (w p)t For some purposes it is very desirable to suppress the main or unmodulated carrier frequency (E sin wt of equation :2), that is, to prevent its transmission. In which case, equation (2) will develop into (5) e=E sin wt+E sin (wt- 120) +15 sin (ob-240)- =E sin wt-0.5E sin tut-0.866113 cos of -0.5E sin wt+0.866E S wt=() that is, the component voltages balance themselves out to zero. If new modulation is effected upon one of the three single phase components, for example. the first term of (5), the latter may be written in the form (6) c =E(1 +K sin pt) sin wt+E sin (wt 120) +1) sin (wt- 240) By trigonometric transformation equation (6) develops into (7) c =E sin wi+KE sin pt sin wt-O.5E sin rat-0.86619 cos wi0.5l& sin wt-HLSGSE cos of v (8) e -zKEsni pt sin (at or cos (w phi-5 w? cos (tim);

which is identical with equation (3), the latter resulting from equation (1) when the resource modulation by voice or otherwise, is cilected upon only one of the phases, the result is that high frequency, currentwill exist in the load circuit, antenna. system, or wires, only during the-period of modulation; the amplitude of this current is directly .prportional to the percentage of modulation iii. if n'iodulation is not taking place K 0, and no high frequency current flows. The resin carrier frequency is thus suppressed.

My invention will be more clearly understood by reference to the uccompanying drawings, in which:

Figure 1 illustrates my invention as ap plied to u space radio transmission system; if; is a rector diagram illustrating the displacement of the high frequency voltages generated at the transmitting station; and Fig. 3 illustrates a. modified. arrangement of transmission system embodying the principles of my invention and showing the energy delivered to any type of load representative of a Wired or space radio system.

Referring to the drawings in detail: In Fig. 1., l have shown an electron tube trans-- mission. system in which reference charac- 1 represents a three phase high frequency generator as, for example, the type shown in my copending application, Serial No.

filed ii unuur 9, 1925. Generator 1 works into coils Q. 3 and connected as shown in V, which term the primary coils of three grid transformers, the secondaries ii, 6 and i ot'which ere also connected in! and then connected uitl'i the grids cit vacuum tubes 8, ii and All grids are shown biased ne ively by battery ll n the positive terminal or, which. is grounded at 12. In series with secondary 7 and the grid oi. tube i) is connected the secondary 13 of an audio It .4 series with the primary 15 is microphone 16 and battery it. Bypassing condenser 18 is connected across the secondary 13 of transformer 14. The filaments of the tubes are trier l indicated as being grounded atone poi y The plates of tubes 8, 9 and it are connected respectively to inductences 15 and 521 through blocking condensers .22, 23? and luductziuces 19, 20 and 21 ore connected in l. the common point of which grounded at 12. The plates. are energized from a high potential source represented by battery 25 through. high i'requency cliolre coils 26. The negative terminal if battery-1253 is grounded at 12. inductiroly coupled to coils 19 5.0 and 21 are secondsry coils 2 25, and which are connected in series in the proper polarity with respect to t 1 antenna anf round 12.

The operation of the Clllllllb is as follows:

lirom omerator l. thronii the coupling be tween tl coils 2 5. 3--6 shri l-7, three equal high :trerpsency voltages, :Iiiti'ering in phase by 1530 d ecomes represented in the Willi-311G} modulating transformer i i. in

vector diagramof Fig. 2, are applied to the grids of amplifying tubes 8, 9 and 10 which are assumed to be approximately similar in their characteristics. lVith the output circuits of these tubes properly adjusted and without modulation at microphone 16, no current will flow in the antenna. circuit due to the three phase balancing action previously described. When modulation takes place, by voice, for example, at microphone 16, the balanced condition is disturbed by virtue ,o'l change in characteristics of tube 10 brought about by impressing an audio frequency voltage in the grid circuit, and a pulse oi high frequency current of the form given by equation 9 will appear in the antenna circuit. The unmodulated carrier frequency is prevented from reaching the antenna, or is suppressed. .1

instead of the load circuit being an air tennu it may be a local series circuit as shown in Fig. i3. and composed of inductance." 2T. .28 and 29. capacity 31', and resistance. 32, representing the characteristics of a line wire system. 1

In Fig. 1 the modulation is ell'ected on the grid of one of the three amplifying tubes in the usual manner. In Fig. 3 is shown a method of effecting modulation on the plate of one tube. In this diagram battery 25 supplies the necessary plate voltage through high frequency choke coils 26 /as before. In series with one of these coils however is a very large iron core inductance 33. The plate of the modulating tube is connected to thc'junction point between inductancc fill and the high frequency choke 26. The grid circuit of tube 34 contains the secondary 35 of a modulation transformer and biasing battery 36. The primary circuit of this transformer contains the primary winding 37. microphone l6, and battery 17. in series with the high frequency choke coils in the D. C. supply to tubes 8 and 9 may be connectcd the resistances 38. the value of which is equal to the direct current resistance 0!? inductance 3-33. The function of resistances 38 is to keep the plate voltage applied to tubes 8 and 9 the same as that applied to tube 10, and thus to assist to maintain the high frequency balance oi the system although it, is not always necessary to employ these resistances.

If amodulating source as, for ezumiple, the voice, acts on microphone 16 in accordance with well known theory, the plate voltage applied to tube 10 will vary in accordance therewith and a pulse of current will. appear in the load circuit, 27, 2-8, 3i and 352. Due to the balanced properties or the sys tem, an upsetting of the balance in this mannor will cause suppression of the umuioduleted component oi": the output current.

llhile l have shown butter-ice in cachet the cathode circuits at buttery for sup plying the anode potential, it will be understood that generators or any other source of energy may be provided and that the symbolic representations are merely for the purpose of illustrating sources of energy. I have illustrated my invention in two ,embodiments, but it is to be understood that the circuit arrangements shown are only for the purposes of illustrations and that the principles of my invention are broadly adapted for various systems inwhich a. source ofmulti phase energy is provided and the energy normall Y oalanced in a plurality of circuits. By unbalancing the circuits by modulating the energy on one of its phases I am enabled to impress high frequency energy upon a work circuit of general application while the unmodulated component high frequency carrier wave is suppressed both during and intermediate the signaling periods. I may utilize various methods at the receiving station for restoring the carrier frequency in order to reproduce the received signals in the proper form.

It is evident from a consideration of the circuits shown in Figs. 1 and 3 and from is proportional to the degree of unhalancing.

For example, equation (6) may be re written in the form (10) e =0.8E(1-l-K sin p1!) Siri (n+1; sin (wt- +11 3 sin z-240 which states mathematically that two of the three phase voltages have minimum values equal to E, while that of the third is (0.815) or is less than that value. Equation (to) expanded in the usual manner yields e =().SE sin wl+(l.8KE sin pt sin wf-().5E sin col 0.86615 cos (at-05E sin wt +0.866E cos wt 0.'2E sin wt 0.8KE sin pt sin wt which is the form of ct nation i. e., con tains an unmodulate carrier frequency component of reduced amplitude.

The slight degree of unbalam-ing may be obtained in practice in a number of ways, for example, by having the coupling at one of the input transformers, 2 6. l-6, or 47, or one of the output iltiIlSfOlHiilS iii-27, 20-2Fh El-29 closer than the coupling of the two remaining transformers, thereby in the first case impressing a higher voltage on the input of one of the amplifying tubes 8, l), 10, or in the second case derelopinp a higher output voltage from one of the amplifying tubes into the load circuit. As actually observed in practice, in a certain three phase generating unit, arbitrarily unbalanced to a slight degree, the root mean square antenna current durinn modulation averaged (L5 ampere while. when not n'iodulat-ing the residual antenna current was 0.03 ampere.

Now under certain conditions of operation it is very advantageous not to complete-- l v suppress the 'unmodulated component of the carrier frequency current but to cause to flow in the load circuit or to transmit both during and intermediate the periods of modulation a small fractional amount of the nnmodulated carrier component. and it is readily seen that this may be accomplished by means of the methods and circuits outlined herein.

- 921*] sin wt COS (w p)t 005((0 pli While the coils 2. 3 and 4, 5, (5 and 7, and 15), 20 and 21 have been shown connected in star (Y), they may also be connected in delta I have illustrated the windings as in ductively coupled but I desire that it be understood that other forms of com iling may be used.

Two methods of modulation have been shown in Figs. 1 and 3. It is not intended, however, to limit the scope of this inven tion to any particular method of 1nodulation, it being; understood that any method of modulation acting on one of the three hases so as to disturb a balanced or semialanccdcondition falls within the scope of the appended claims.

hat I claim as new and desire to secure by Letters Patent oi the United States is as follows: p

i. In a high frequency signaling system, the combination oi" a source of three phase high frequency current, a work circuit, signaling means associated with said source, the said high fretpwncy source, work circuit and signaling means being so associated that both duringhnd intermediate the signaling periods, that, component of the high frequency current which unaffected by the signaling means is suppressed from said work circuit.

:2. In a high frequency signaling system, the combination of a source of multiphase high frequency CILLTGUL a work circuit. sig

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menses cuitand signaling means being so associated a balanced i :i s

that both during and intermediate the signaling periods, that component of the high frequency current which is unaffected by the signaling means is suppressed from said work circuit.

3. In a high frequency power systennthe combination of a three phase source of high frbquency current, a plurality of electron tube amplifier circuits, corresponding in number to the number of phases. of said source, so associated with said source as to increase the amount of high frequency energy supplied by each phase of the three phase source, a load circuit associated with said electron tube circuits in such a manner as to absorb the high frequency power dcveloped by said circuits, a means of modulation associated witlr one of said electron tube circuits, said combination so arranged that both during and intermediate the pcriods of modulation the unmodulated component of the high frequency current is suppressed from said load circuit, but that during said modulation periods, completely modulated high frequency current will flow in said load circuit.

4. In a high frequency system, the com.-

bination of a three phase source of high frequency energy, a work circuit associated with said source, a modulating means associated with one of the phases of said source, the said three phase source, work circuit and means of modulation so arranged that both intermediate and during the periods of modulation, the unmodulated component of the high frequency current is prevented from flowing in said load circuit, but that during modulationcompletely modulated high frequency current will flow in said load circuit.

5. In a high frequency signaling system the combination of a three phase source 0 high frequency energy, a plurality of inductanccs connected in Y and energized from said three phase source, a plurality of electron tube circuits corresponding in number to the number of phases of said source, an input circuit for each of said electron tube circuits, inductances in each of said input circuits, said in'ductances being con-- nected in Y and inductively coupled with said aforementioned inductances, an out put circuit for-each of said electroii tube circuits, inductances in each of said output circuits, said inductanccs being connected in Y, a worlr inductively coupled with said inducz an in said output circuits, said elcc its being normally "(sat with full high L ied from the three the input circuits of said circuits all energy is supfrequency en phase source electron tut.

pressed from said work circuit, modulating means associated withonc of said electron tube circuits in such manner that when modulating energy supplied, the balanced condition of said electron tube circuits is disturbed and high frequency energy is supplied to the load circuit only during the period of modulation.

(l. in a high frequency signaling system the combination of a source of three phase high frequency energy for generating a carrier frequency, a work circuit, signaling means for impressing said energy on said work circuit, and means whereby said energy becomes ineffective to excite said work circuit intermediate the periods ofoperation of said signaling means for suppressing that component of the carrier frequency which is unaffected by said signaling means from said work circuit.

'7. In a high frequency electrical system the combination of a substantially balanced source of three phase high frequency energy, a work circuit, and means for disturbing the substantially balanced condition of said. source for impressing high frequency energy on said work circuit.

8. In a high frequency signalin system the combination of a substantially alanced source of multiphase high frequency energy, a work circuit, and means connected with one of the phases of said substantially balanced source for disturbing the balanced condition of said source whereby high frequency energy may be impressed on said work circuit.

9. In a high frequency signaling system the combination of a source of multiphase high frequency energy, a circuit in which said energy is normally substantially balanced, a work circuit connected with said aforementioned means, and signaling means for unbalancing the substantially balanced condition of said first mentioned circuit whereby signaling energy is impressed upon said work circuit.

10. A high frequency signaling system comprising incombination a source of multiphase high frequency energy, a plurality or electron tube circuits corresponding in numher to the number of phases of said high frequency source, a work circuit, connections between said wort: circuit and each 0t said electron. tube circuitgsaid clectroi 'ube circuits being normally substantially balanced in such manner that ei'icrgy from rid multi phase source is prcreniml from reaching said work circuit, and means for unbalancing the substantially oalancrd rendition of said electron tube circuits whereby high frequency energy may beiinpmssed upon said work circuit.

11. {r high frequency signaling system comprising 2n .wmhination a source of raulti phase high frequency energy, a plurality of electron tube circuits corresponding in number to the number of phases of said high frequency"source, a work circuit, connections between said work circuit-and each of said electron tube circuits, said electron tube circuits being normallysubstantially balanced in such manner that energy from said multiphase source is prevented from reaching said work circuit, and means connected with one of said electron tube circuits for unbalancing the substantially balanced condition of said electron tube circuits whereby signaling energy may be impressed upon said work circuit.

12. A high frequency signaling system comprising in combination a source of multiphase high frequency energy, a plurality of electron tubes corresponding in number to the number of phases of said high frequency .-'Ourcc, an input and output circuit associated with each of said electron tubes, an induc tancc in each of said input and output circuits, means connecting the inductanccs in said input circuits separately with the phases of said multiphase source, a work circuit, means connecting the. inductances in each of said output circuits with portions of said work circuit, said input and output circuits being normally substantially balanced in such manner that with high frequency electrical energy supplied from the multiphase source to said electron tubes s1| b stantially all of said energy is suppressed from said work circuit, and means for unbalancing the substantially balanced condi t-ion of said input and output circuits whereby high frequency energy may be impressed upon said work circuit.

13. A high frequency signaling system comprising in combination a source of multiphase high frequency energy, a plurality of electron tubes corresponding in number to the number of bases of said high frequency source, an input and output circuit associated with each of said electron tubes, an inductance in each of said input and output circuits, means connecting the inductances in said input circuit separately with the phases of said multiphase source, a work circuit, means connecting the inductances in each of said output circuits with portions of said work circuit, said input and output circuits being normally substantially balanced in such manner that with the entire high frequencyenergy supplied from said source substantially all of said energy is suppressed from said work circuit, and means connected with the circuits of one of said electron tubes whereby the' balanced condition of said input and output circuits may be unbalanced for impressing signaling energy upon said work circuit.

it. a e high frequency signaling system the combination of a three phase source of high frequency signaling energy, a plurality of inductances connected inY and energized from said three phase source, a plurality of electron tube circuits corresponding in number to the number of phases of said source, an input circuit for each of said electron tube circuits, inductances in each of said input circuits, said inductances being connected in Y and inductively coupled with said aforementioned inductances, a work circuit, connections between said work circuit and said electron tube circuits, said electron tube circuits being normally substantially balanced in such manner that with the total high frequency energy supplied from said source to said electron tube circuits substantially all high frequencv electrical energy is suppressed from sai work circuit, and means connected with one of said electron tube circuits for unbalancing the substantially balanced condition of said electron tube circuits whereby signaling energy may be impressed in said work circuit.

15. In a high frequency signaling system the combination of a three phase source ofhigh frequency signaling energy, a plurality of induetances connected in and energized from said three phase source, a plurality of electron tube circuits corresponding in number to the number of phases of sa1d source, an input circuit for each of said electron tube circuits, inductances in each of said input circuits, said inductances liein connected in Y and inductively couple with said aforementioned inductances, a work circuit, connections between said work circuit and said electron tube circuits, said electron tube-circuits, being normally substantially balanced in such manner that the carrier frequency current component of the high frequency signaling energy is suppressed trom said Work circuit, and 1nodulation means for unbalancing the balanced condition of said electron tube circuits whereby the modulation current component of the signaling energy may be impressed upon said work circuit.

16. In a high frequency signaling system the combination of a multiphase source of high frequency signaling energy, circuits connected with said multi 'ihasecource for normally substantially balancing the energy supplied therefrom, a, single phase work circuit, connections between said single phase work circuit and said aforementioned circuits, and means for unbalancing the normally substantially balanced condition of said first mentioned circuits whereby high frequency signaling energy may be impressed upon said single phase work circuit.

17. In a high frequency signaling system the combination of a multiphase source of high frequency signaling energy, circuits phases for unbalancing' the substantially balconnected with said multiphase source for anced condition of said firstmentioned cirnormally substantially balancing the'energ cui ts whereby high frequency signaling en-- 10 supplied therefrom, a single phase work cirergy may be impressed upon'said Work circuit, connections between said single phase cuit. work circuit and said aforementioned C11- c'uit-s, and means connected with one of said ROBERT D. DUNCAN, JR.- 

